Many different designs of three-dimensional laser scanner instruments exist. Some of these instruments reach a very high precision, but can require precise alignment and long measurement times. Many possible applications for such instruments are conceivable in consumer products, when both costs and the degree of complication of their operation can be reduced.
Although concepts exist for LIDAR imagers which avoid mechanical actuation of optical elements to steer illumination light beams and to collect the light scattered in the scene (such as disclosed e.g. in PCT application PCT/EP2011/065267), designs using mechanically moving optical elements (such as disclosed e.g. in WO2011/117206, PCT/EP/2011/057192 or PCT/EP2011/062314) are widespread. Typically today's commercial laser scanner devices relying on mechanical systems to scan the laser beam use gimbal-mounted mirrors, rotating reflectors, or counter-rotating prism pairs. This leads to rather voluminous, often noisy and expensive instruments.
In scanner devices which use the same light path for detection as for illumination, increasing the optical aperture for detection to improve the light gathering ability of the system means the same increase in aperture of the optical elements in the illumination path, where it is typically not required. Since size and weight of the optical elements increases accordingly, this can result in even more cumbersome constructions and sluggish performance when the laser beam is scanned by mechanical actuation of optical elements.
For this and other reasons, like improved capabilities in foggy or dusty situations, separate light paths for illumination and detection are preferable. When the optical system responsible for the scan of the illumination beam can be designed without restrictions regarding the detection of the light scattered in the scene, compacter and faster designs using for example micro-electro-mechanical-system (MEMS) technology, optical fiber technology with miniaturized optics and actuators become possible.
Lateral spatial selectivity in the detection process is naturally given to a certain extend in systems with partially overlapping light paths for illumination and detection. Using separate light paths for illumination and detection gives the freedom to design both light pathways in a way optimized to their respective purpose, but a lateral spatial selectivity in the detection has to be provided for separately. When detector arrays such as CCD, CMOS or micro-bolometer sensors can be used, lateral resolution is readily given and most functionalities described for this invention can be implemented by software processing of the acquired image data.
The present invention is particularly valuable for scanner systems which offer very little or no transversal resolution and selectivity by the light detector itself as is the case when a single detector element is used. Reasons for this can be the increased sensitivity and/or time resolution of single detectors as compared to CCD, CMOS or micro-bolometer detector arrays, as well as cost considerations and availability at the working wavelength.